Mike Carp motioned toward the locker next to his, a gesture of both deference and deprecation. If he could do it, why can’t I, Carp seemed to suggest. It was Daniel Nava standing next to him, and the topic was learning a new position in spring. Last year, Nava put on a first baseman’s mitt for the first time in his professional career, and it paid immediate dividends for the Red Sox during the season. Nava proved himself an at-worst adequate defender at the bag, lending Boston greater defensive versatility. Nava ended up starting eight games at first and playing 86 innings there overall on the year. Carp saw how much learning a new position helped Nava, and so he approached Brian Butterfield with an idea the first day of workouts. How about a few ground balls at third base? “It’s something that I’m familiar with but not completely familiar with,” said Carp, who played a dozen games at third in the Gulf Coast League and Single-A South Atlantic League while in the Mets system nearly a decade ago. “The way our coaching staff prepares us, if I can get with them and shadow Will [Middlebrooks] and watch those guys do their business, who’s to say I can’t get a few at-bats at third this year?” It’s a no-risk move for Carp, who’s not quite a natural defender in left field or at first base. Third base is a spot where the Red Sox are lacking in depth — even utilityman Jonathan Herrera is shallow in experience at the hot corner — and Carp is itching for a chance to see more playing time. Remember, Brock Holt and Xander Bogaerts each played third base last season for Boston, and neither had any experience at the position before spring training. “We’re keeping it open,” Carp said. “I’m definitely excited for the challenge. It’s definitely opening up a new door. As long as I can work hard, who knows?” Butterfield and Carp had their first session of extra work at third on Saturday. “He caught the ball well,” said Butterfield. “He’s at a point where he’s comfortable with the environment, he’s played well for us. We’re more than willing to see what he looks like over at third base.”